Configures namespace deletion
Configures namespace deletion

Add option to the L3 and DHCP agent configuration to
enable automatic deletion of router and DHCP namespaces
when the router or network is deleted.

Change-Id: I75d5eb4bac4b1d163b44f7ea27db01b62a80bedd
backport: Juno
Closes-Bug: 1404941

saeki-masaki/openstack-manuals,kairoaraujo/openstack-manuals,saeki-masaki/openstack-manuals,gongysh2004/openstack-manual,gongysh2004/openstack-manual,openstack/openstack-manuals,AlekhyaMallina-Vedams/openstack-manuals,AlekhyaMallina-Vedams/openstack-manuals,potsmaster/openstack-manuals,AlekhyaMallina-Vedams/openstack-manuals,openstack/openstack-manuals,Akasurde/openstack-manuals,Akasurde/openstack-manuals,openstack/openstack-manuals,openstack/openstack-manuals,potsmaster/openstack-manuals,kairoaraujo/openstack-manuals